Engine combustion using gasoline fuel may generate particulate matter (PM) (such as soot and aerosols) that may be exhausted to the atmosphere. To enable emissions compliance, particulate filters (PF) may be included in the engine exhaust, to filter out exhaust PMs before releasing the exhaust to the atmosphere. Such devices may be periodically or opportunistically regenerated during operation of an engine to decrease the amount of trapped particulate matter. Regeneration is typically achieved by raising a temperature of the PF to a predetermined level for a sustained period, while flowing exhaust gas of a defined composition through the PF in order to burn or oxidize the trapped particulate matter. During engine start-stop (idle stop) conditions, deceleration fuel shut-off (DFSO) conditions, and periods of vehicle operation using machine torque, there may not be sufficient time for completing regeneration of the PF.
Various approaches are provided for regenerating a PF during engine shut-down conditions. In one example, as shown in U.S. Pat. No. 8,844,272, Bidner et al. disclose a method for operating a vacuum pump coupled to the engine intake manifold to route ambient air via the engine exhaust manifold during engine-off conditions. Oxygen in the ambient air flowing through the PF may facilitate in regenerating the PF during engine-off conditions when the temperature of the PF is above a threshold temperature.
However, the inventors herein have recognized potential disadvantages with the above approach. As one example, operating the intake vacuum pump to draw in ambient air from the exhaust manifold may be a time consuming process due to the time required for a vacuum to build up in the exhaust manifold. A high powered pump may be desired to remove air from the exhaust system and the EGR passage for vacuum generation. By the time sufficient oxygen from ambient air reaches the PF, the temperature of the exhaust passage including the PF may reduce below a threshold temperature as desired for PF regeneration. Incomplete PF regeneration may cause a higher than desired amount of PM to remain on the PF, thereby increasing exhaust back pressure which may adversely affect engine performance during subsequent engine cycles.
The inventors herein have identified systems and methods by which issues with the above approaches are resolved. One example method comprises, method, sing: during a non-combusting condition of an engine coupled to a vehicle, responsive to a higher than first threshold soot load on a particulate filter (PF) coupled to an exhaust passage of the engine and a PF temperature greater than a threshold temperature needed for soot oxidation in presence of oxygen, activating an electric booster in an intake system of the engine to rout: compressed air to the PF for PF regeneration. In this way, by operating an electric booster during engine non-combusting conditions, a motive force may be provided to route compressed air via the PF for PF regeneration.
In one example, the PF may be opportunistically regenerated during an engine non-combusting condition. The engine may be a boosted engine comprising a turbine driven intake air compressor and an electrically driven intake air compressor (herein also referred to as a battery operated electric booster) that is selectively operated for providing additional boost during increased torque demand. If during an engine non-combusting condition, engine start-stop condition, deceleration fuel shut-off (DFSO) condition, and a period of vehicle operation using machine torque, it is estimated that the PM load on the PF is higher than a threshold load and a temperature of the exhaust passage including the PF is higher than a threshold temperature, PF regeneration may be initiated. The intake throttle may be actuated to a completely open position and the electric booster may be activated to flow compressed ambient air from the engine intake passage to the PF. An exhaust gas recirculation (EGR) valve coupled to an EGR passage may be opened and also a wastegate valve coupled to a wastegate passage may be opened to facilitate flow of compressed air from the intake manifold to the exhaust manifold. At the elevated temperature, in the presence of oxygen from the compressed air, the PM may be burnt and the PF may be regenerated. The compressed airflow may provide the motive force to flow heated air from an exhaust catalyst coupled to the exhaust passage upstream of the PF to the PF to further expedite the regeneration. Flow of compressed air may be continued until one or more of the PF regeneration being complete, the PF temperature reducing below the threshold temperature, and initiation of engine combustion.
In this way, by opportunistically using existing engine components, such as an electric booster, regeneration of a particulate filter may be carried out even during engine non-combusting conditions, thereby eliminating the need for additional engine components. By using an electric booster, compressed air with a high oxygen content may be supplied to the PF within a short duration after engine shut-down. The technical effect of carrying out particulate filter regeneration during an engine-off condition is that for hybrid vehicles with short engine run-times, a clean PF may be maintained, thereby improving emissions quality and engine performance. In this way, residual exhaust heat may be optimally utilized for PF regeneration.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.